Publish the package to npm

[Abioladory123]

Summary

The package is named @novatip/sdk and is not on the registry, so nobody
outside this organisation can install it. The backend and frontend both depend
on it through a relative path to a sibling checkout, which is why CI in those
repositories has to check this repository out and build it first.

Everything else is already in place: the exports map, the ESM, CommonJS and
declaration outputs, and the prepublishOnly script that typechecks and builds.

Acceptance criteria

• The package is published under a stable version and installs cleanly in a
  fresh project.
• Both ESM and CommonJS entry points resolve, and types are picked up.
• The README install instructions match what actually works after
  publishing.

Getting started

Fork this repository, clone your fork, and add this repo as upstream:

git clone https://github.com/<your-username>/novatip-sdk.git
cd novatip-sdk
git remote add upstream https://github.com/Novatip/novatip-sdk.git
npm install

Create a branch for this issue:

git checkout -b chore/publish-to-npm

Suggested commit message:

chore: publish the package to npm

Run npm run lint, npm run typecheck, and npm run build before pushing, then open a pull request from your fork against main and link this issue. See the contributing guide for the full workflow.